In general, as a main motor for a railroad vehicle, a main motor of a totally enclosed type (a totally-enclosed main motor) is often adopted from the viewpoint of maintenance saving. The totally-enclosed main motor includes: a frame formed in a cylindrical shape, on the inner circumference side of which a rotor is disposed; and brackets disposed at both ends of the frame so as to oppose each other and to rotatably support a rotor shaft. A bearing is provided in the center of the brackets. A cylindrical rotor core, which houses a stator coil, is attached to an inner circumferential section of the frame. A uniform air gap is provided between the inner circumferential surface of the stator core and the outer circumferential surface of the rotor.
In the totally-enclosed main motor configured in this way, the outdoor air cannot be directly taken into the motor to cool the motor because of a structure for sealing the inside of the motor. To radiate heat in the motor to the outside, measures for, for example, increasing a heat radiation area are necessary. There is a disadvantage that an apparatus is increased in size. Therefore, to eliminate this disadvantage, there has been proposed a totally-enclosed main motor in which a cooling fan is used as a component that partitions the inside and the outside of the motor.
In the totally-enclosed main motor, the cooling fan, which partitions the inside and the outside of the motor, and a frame are in a relation of a rotating section and a fixed section. Therefore, it is necessary to provide a labyrinth between the cooling fan and the frame. Therefore, there is a problem in that dust or water slightly intrudes into the motor via the labyrinth.
To solve such a problem, in the conventional main motor described in Patent Literature 1, grease equivalent to or similar to bearing lubrication grease is applied to and filled in the labyrinth to prevent the intrusion of dust and the like.